The present invention relates, in general, to vibrator systems and, more particularly, to assemblies for transmitting vibratory motion to a device, such as an electrostatic precipitator, under temperature conditions that may be as high as 800.degree. F.
Pneumatic vibrators are widely used in industry to facilitate movement of bulk materials through bins and hoppers, deslagging boilers, and in electrostatic precipitators, to knock accumulated dusts off the collecting plates therein. The piston-driven vibrator terminates in a sleeve having a tapered bore, into which a transmission pin fits, which is variously called a precipitator pin or a rapper rod. This pin is tapered at both ends to fit into the vibrator sleeve and a similar sleeve and housing on the anvil holding the precipitator plates.
To achieve electrical isolation, the rapper rod must be a good insulator, an ability to withstand electrical charge of 60,000 volts DC being a typical specification.
The rapper rod must have a high mechanical strength; rapping rates can vary from 1500 to over 2500 impacts per minute, and the inner impact power, in foot-pounds per second, can vary from 5 to over 3,000.
More recently, these rigorous specifications have been further complicated by the desire of utilities, and other industrial concerns to operate precipitators at very high temperatures, up to 800.degree. F., mainly to get good dispersion of cleaned stack gases and avoid condensation, and also avoid the expensive reheating that is required if the gases are scrubbed at lower temperatures.
Metal rods are of course ruled out by the electrical requirements. Rods fabricated from fiber-glass impregnated melamine plastic have been employed with success, but only on units operating below about 300.degree. F., above which that material loses its mechanical strngth.
For applications at very high temperatures, ceramics are an obvious material of choice, but great difficulty with fracture has been experienced even with tapered sleeves and housings, wherein the impact energy is absorbed over a much larger surface area than would be the case with simple end-rapping.
A further problem has been the need to retro-fit existing precipitator installations for high temperature operation with impact-resistant ceramic rapper rods where machining of sleeves or the like is not possible.
Not all vibrator assemblies include tapered sleeves, which are essential for the present invention; one line that does is produced by National Air Vibrator Co. under their "Rapper-3" brand, and is described in U.S. Pat. No. 3,731,907.